If you’re one of the millions currently downloading Windows 7 RC, you’re very soon (well, I say very soon – if our experience is anything to go by, you might have completed the download by Thursday week) going to be presented with a dilemma: Perform a clean install or hack the OS and upgrade in place over the beta.

Microsoft’s installation instructions tell a little white lie. “If you’ve installed Windows 7 Beta on your PC, you’ll need to back up your data, and do a clean installation of the RC,” they claim. Not true. That might be what Microsoft wants you to do, but it is perfectly possible to upgrade your beta by following the instructions provided on Microsoft’s own Engineering Windows 7 blog.

Microsoft doesn’t want you to do this, of course, and for perfectly valid reasons. In the real world, when Windows 7 is finally released, few people are going to be upgrading from one version of Windows 7 to another. It wants as many people as possible testing the upgrade process from Vista, not discovering and reporting bugs from one build to another.  

However, if like me and our editor Tim Danton, you simply can’t be bothered to reinstall all your apps, you can upgrade in place by hacking the version number of the RC before attempting an installation (click on the Engineering Windows 7 link above for full step-by-step instructions).

Originally I thought upgrading in place would be a time-saver. No need to dig out the Office discs, re-download Firefox, configure UAC to my liking etc. However, the upgrade took over an hour-and-a-half compared to the 20 minutes or so it took my colleagues to do a clean install, wiping out the smug notion of efficiency I was harbouring. 

What’s more (and this is only anecdotal evidence so far), Windows 7 seems to run a smidgin slower on the upgraded machines. Start-up and shut-downs seem a few seconds more sluggish, it doesn’t spring into life the instant you enter the admin password, and there’s the odd graphical slowdown with the Aero interface. It’s nothing to scare the chickens, but just enough for us upgraders to come in this morning and ask “does it feel a bit slower to you?”. 

So does upgrading in place work? Yes. Would we recommend it? Probably not. On this occasion, it might just be better to do as Microsoft tells you.